The diversification of several genes involved in reproduction is promoted by positive Darwinian selection. However, the selective force(s) driving their divergence remains unknown. It is likely that the interaction between male and female reproductive proteins drives this rapid divergence. I will examine the selective forces driving the divergence of reproductive genes in Drosophila. Drosophila males transfer approximately 100 accessory gland proteins (Acps) to females during, 18 genes encoding Acps have been reported from D. melanogaster. Acps are rapidly evolving, increase the female's egg laying rate, reduce female receptivity to further mating, promote sperm storage in female, mediate sperm storage, and as a by product of these beneficial effects reduce the females lifespan. The first aspect of the proposed research is to identify female receptors Acps. Identifying their female binding partners will lead to insights to the function and selective forces promoting the rapid evolution of these male proteins. The second aspect involves analyzing these male and female reproductive genes in an experimental population of Drosophila in terms of sequence evolution and biochemical function to test a hypothesis proposed to account for the divergence of reproductive genes. Finally, an EST project will be completed to identify all Acp genes. The experimental methods used in the EST project allow an in depth analysis of the evolution of all proteins in this male reproductive tissues. This will provide insights into the type of reproductive molecules, which are rapidly evolving.